Molecular Biology 1-3

put together by: Linda Fahlberg-Stojanovska

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• Carbohydrates

• Lipids

• Amino Acids

Contents

Carbohydrates = Saccharides

• The term carbohydrate = saccharide in biochemistry.

• The carbohydrates (saccharides) are divided into four

chemical groupings:

– monosaccharides = simple sugar

– disaccharides (2 simple sugars)

– oligosaccharides (3-6 simple sugars) and

– polysaccharides (>6 simple sugars = macromolecule)

• monosaccharides and disaccharides = sugars

Carbohydrates = Saccharides

• A carbohydrate is an organic compound; it consists only of carbon,

hydrogen, and oxygen.

• General formula is: Cm(H2O)n with H:O atom ratio of 2:1 (like water).

• However, there are exceptions to this. One common example would

be deoxyribose, a component of DNA, which has the empirical

formula C5H10O4.

• Carbohydrates are not technically hydrates of carbon. Structurally it

is more accurate to view them as polyhydroxy aldehydes and

ketones.

• Monosaccharides and disaccharides are called sugars and are

“small molecules”; polysaccharides are large or “macromolecules”.

Chirality

• Chiral molecule is NOT superposable on its mirror

image.

– It lacks an internal plane of symmetry and thus is not

superposable on its mirror image.

– Chiral molecules usually have an asymmetric carbon atom.

An achiral (non-chiral,

symmetric) molecule and its

enantiomer (mirror image).

http://en.wikipedia.org/wiki/Chirality_%28chemistry%29

Monosaccharide = Simple Sugar• Monosaccharides or simple sugars are the most basic

units of biologically important carbohydrates.

• Monosaccharides are monomers. They are used to build disaccharides such as sucrose and polysaccharides (such as cellulose and starch).

• Usually colorless, water-soluble, crystalline solids.

• Examples: glucose, fructose, galactose, xylose and ribose.

• Further, each carbon atom that supports a hydroxyl group (except for the first and last) is chiral, giving rise to a number of isomeric forms all with the same chemical formula.

• For instance, galactose and glucose are both aldohexoses, but have different chemical and physical properties.

Monosaccharide = Simple Sugar

glucose fructose

Monosaccharides - Chirality

glucose galactose

Disaccharides• A disaccharide is the carbohydrate formed when two

monosaccharides undergo a condensation reaction and

bind together in one molecule.

• As we shall see, a condensation reaction is a

synthesis or anabolic reaction that releases water.

• Common disaccharides are sucrose, lactose and

maltose.

• As we shall see, the bond formed between the 2 simple

sugars of a disaccharide is called a glycosidic bond.

Disaccharide – Maltose α(1-4)

H2O

glucose glucose

disaccharide glycosidic bond

maltose

Lipids• Lipid is a group of naturally occurring molecules

– fats = triglycerides

– steroids • steroid hormones

• subgroup sterols (example: chloresterol)

– phospholipids

– fat-soluble vitamins (such as vitamins A, D, E, and K),

– monoglycerides,

– diglycerides

– others.

LipidsThe main biological functions of lipids include

• energy storage

fat (adipose tissue)

• structural components of cell membranes phospholipids, cholesterol, ...

• important signaling molecules

steroid hormones, prostaglandins

Lipids – Classification 1

http://www.fao.org/docrep/field/003/AB470E/AB470E03.htm

Fatty Acids

Fatty acid issimplest lipid

http://www.biochem.arizona.edu/classes/bioc462/462a/NOTES/LIPIDS/Lipids.html

Fats = Triglycerides• All fats are derivatives of fatty acids and glycerol.

• The molecules are called triglycerides, which are esters of glycerol and 3 fatty acids.

• an ester is molecule formed from the reaction of the – carboxylic acid and an

– organic alcohol

http://en.wikipedia.org/wiki/Fat

If “straightened”, the fatty acids would each be a horizontal line; the glycerol "backbone" would be the vertical line that joins the 3 horizontal lines.

Esters Glycerol + Fatty Acids

http://www.mhhe.com/biosci/pae/botany/uno/graphics/uno01pob/vrl/

The hydrophobic

tail of a phospholipid

•glycerol

•2 fatty acids

Glycerol (3-C alcohol)

• Glycerol is an alcohol with multiple hydroxyl OH groups.

• The glycerol backbone is central to all glyceride lipids.

http://en.wikipedia.org/wiki/Glycerol

Keywords• An alcohol is an organic compound in which the hydroxyl

functional group (-OH) is bound to a carbon atom and this carbon center is saturated, having single bonds to three other atoms.

• Alkanes (saturated hydrocarbons) compounds that have only hydrogen and carbon atoms and have ONLY single bonds (saturated compounds). The simplest alkane is methane CH4.

• Cycloalkanes (naphthenes) are types of alkanes that have one or more rings of carbon atoms (all with single bonds). Steroids have four cycloalkane rings.

Steroids• Steroid is an organic compound with a characteristic

arrangement of four cycloalkane rings

• The core of steroids is ≥17 carbon atoms bonded together: – 3 cyclohexane rings A, B, C and 1 cyclopentane ring D

– steroids vary by functional groups attached to this four ring core and by the oxidation state of the rings

• Examples:– Hormones and sterols

http://en.wikipedia.org/wiki/Steroid

Steroids

http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookchem2.html

Steroids – Sterols - Cholesterol• Sterols are special forms of steroids,

• with a hydroxyl group at position-3 and

• a skeleton derived from cholestane

• Examples: Vitamin D and Cholesterol

http://www.cytochemistry.net/cell-biology/membrane_intro.htm

• Cholesterol = build and maintain membranes

– hydroxyl group on cholesterol interacts with the polar head

groups of the membrane phospholipids and sphingolipids,

– bulky steroid and the hydrocarbon chain are embedded in

the membrane, alongside the nonpolar fatty acid chain of

the other lipids.

• Cholesterol reduces the permeability of the plasma

(cell) membrane so only neutral solutes, protons H+ and

sodium ions can pass through.

Cholesterol

Cholesterol• Within cell membrane, cholesterol also functions

intracellular transport, cell signaling and nerve conduction.

• Within cells, cholesterol is the precursor molecule.

• Cholesterol is an important precursor for the synthesis of vitamin D and for the steroid hormones.

• In the liver, cholesterol is contained in bile.

Cholesterol - Steroid Hormones

• Steroid hormones are derived from cholesterol

• Sex hormones– Progesterone

– Testosterone

– Estradiol

• Aldosterone

• Cortisol

Membrane Lipids

• Membrane lipids are lipids in the cell membrane. Ex: phospholipids, glycolipids, and cholesterol

http://publications.nigms.nih.gov/insidethecell/chapter1.html

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Phospholipid

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http://en.wikipedia.org/wiki/Phospholipid

Bile – Digestion of Lipids• Bile is mostly of water (85%) and bile salts (10%)

• Bile salts solubilize fats in the digestive tract and aid in the intestinal absorption of fat molecules as well as the fat-soluble vitamins, A, D, E, and K.

http://en.wikipedia.org/wiki/Bile

Bile salts surround fat

(lipid) to solubilize it.

http://www.hcc.mnscu.edu/chem/V.27/amino_acid_structure_2.jpg

Amino acids are molecules containing an amine group, a carboxylic acid group, and a side-chain that is specific to each amino acid.

The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen.

Amino acids

Structure of an amino acid

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Side chain = H so it is smallest of the 20 amino acids

•Its codons are GGU, GGC, GGA, GGG•M = 75 g/mol. Solubility=250 mg/ml•Not essential. Can be manufactured artificially and in the body.•Glycine is a colourless, sweet-tasting crystalline solid.•It is achiral (not chiral); all other amino acids are chiral.•It can fit into hydrophilic or hydrophobic environments, due to its two hydrogen atom side chain.

Amino acids - Glysine

http://www.daviddarling.info/encyclopedia/G/glycine.html

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Amino acids - Lysine

• Lysine is an essential amino acid, (human body cannot synthesize it).

• Lysine's codons are AAA and AAG.

• Lysine is a base

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Amino acids - 1

http://www.geneinfinity.org/sp/sp_aaprops.html31

Amino acids - 2

http://www.geneinfinity.org/sp/sp_aaprops.html32